Macroevolution
- Microevolution happens at the population level (natural selection, genetic drift, gene flow)
- Macroevolution: Speciation events form evolutionary independent populations
- New species are the bridge between evolution within a population and larger patterns in evolution, such as new taxonomic groups
How/Why species form: The limits of human cognition
What actually is a “Species”?
- Textbooks: A group of populations whose members have the potential to interbreed in nature and produce viable offspring
What actually is a “Species”?
- Textbooks: A group of populations whose members have the potential to interbreed in nature and produce viable offspring
Biological Species Concept: Unity of reproduction
- Reproductive isolation between populations results in a lack of gene flow
- what are the consequences of no gene flow?
- Individuals do not interbred with other populations or are unable to produce viable offspring after mating
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BSC: Members of a biological species are united by the potential ability to be reproductively compatible
Mechanisms of reproductive isolation? (Fig 24.3)
Issues with the biological species concept
- How do we effectively evaluate isolation?
- Is this even possible in fossils?
- Geographic proximity: how do we know if they cant make babies?
- Asexual reproduction
- Belloid rotifers haven’t reproduced sexually for > 80 million years
- An estimated 2000 species of asexual rotifers are known
Morphological Species Concept: Unity of body plans
Issues with the morphological species concept
- Applies to all organisms but…. what kinds of traits & how many?
- Subjective to the scientist!
- Species can change their form: Polymorphisms
- Cryptic species that do not differ in morphology
- lots of mimics in nature!
Phylogenetic Species Concept: Unity of ancestry
How new species arise: Allopatry
Allopatric speciation in Hawaiian fruit flies
Allopatric speciation in shrimp
How new species arise: Sympatry
